Well I'd love to see other people doing the new clip, so here are my thoughts:
When bouncing off a ceiling then hitting a clipping pixel (the exact seam between two sprite blocks,) the game does a calculation that dictates if you “clip” or simply bounce off the wall/pipe. This method was done because the block next to the pipe has a “p-switch” inside of it that pops out when it is hit. After hitting a block with a p-switch inside, a clip is impossible (99.9% sure) which is why we would activate the block and then attempt to clip through by jumping Mario's head into the activated p-switch block. This resulted in about a 1-in-15 to at times 1-in-50 chance of getting it for me. That's mostly because I'm terrible at visually jumping into the same pixel consistently.

New way:
https://youtu.be/QCns234-XI4
If you duck jump so you don’t hit the block, the game doesn’t know that you just came from a ceiling. If you let go of duck (very important) in the middle of a jump, you stand up instantaneously upon hitting a clipping pixel. Because the game doesn’t see you as coming from a bounce off a ceiling, all it knows is that you stood up and were beneath a block which 100% of the time forces you to clip. This then becomes execution based and not luck based. Again, I'm no Tompa so take this for what it is. One guy's opinion. My only support is that I've never seen myself hit the clipping pixel and bounce off since I started doing it this way. Maybe Im just unobservant though.

Here is a picture where I show my visual sight cues. http://imgur.com/a/mJAE0 I try to start ducking 3/4 of the way through running past the brown block and then I jump as soon as possible after ducking. My sight cue for pressing down and jumping is the red line and the purple line is closer to where I actually end up, and want to end up jumping. Basically, your visual cue for starting your duck jump should be whatever position lets you actually jump just after stepping onto the white rectangle.
As for the jumping technique, I had to find a way to make a very small jump, but not quite as small as the jump I do when I jump over the turtle in the beginning of the level. That jump wouldn't get high enough vertically  to hit the clipping pixel. What I try to do, and your mileage may vary, is run while holding the B button with the tip of my thumb. Then when it is time to jump, I roll from the tip of my thumb to the base of my thumb and keep the rolling motion going until my thumb is completely off the jump button. When done quickly, this does slightly more than a 1 frame jump which is what we are looking for.

I would recommend practicing your own short hop techniques and adjusting your visual cues(where you press down and jump) to match your own reaction times and finger comfort levels.  I'm starting to approach 30% consistency for a first try clip in runs and at times have pushed past 50% over the course of 20+ attempts in practice. If I can do it, anyone can.